Dielectric film and method of forming it, semiconductor device, non-volatile semiconductor memory device, and production method for semiconductor device

ABSTRACT

In a film formation method of a semiconductor device including a plurality of silicon-based transistors or capacitors, there exist hydrogen at least in a part of the silicon surface in advance, and the film formation method removes the hydrogen by exposing the silicon surface to a first inert gas plasma. Thereafter a silicon compound layer is formed on the surface of the silicon gas by generating plasma while using a mixed gas of a second inert gas and one or more gaseous molecules, such that there is formed a silicon compound layer containing at least a pat of the elements constituting the gaseous molecules, on the surface of the silicon gas.

TECHNICAL FIELD

The present invention relates to a semiconductor device in which anoxide film, a nitride film, an oxynitride film, and the like, is formedon a silicon semiconductor, and the formation method thereof.

BACKGROUND ART

The gate insulation film of a MIS (metal/insulator/silicon) transistoris requited to have various high-performance electric properties andalso high reliability, such as low leakage current characteristic, lowinterface state density, high breakdown voltage, high resistance againsthot carriers, uniform threshold voltage characteristic, and the like.

In order to satisfy these various requirements, the technology ofthermal oxidation process has been used conventionally as the formationtechnology of the gate insulation film, wherein the thermal oxidationtechnology uses oxygen molecules or water molecules at the temperatureof about 800° C. or more.

It should be noted that a thermal oxidation process has been conductedconventionally after conducting a preprocessing process of removingsurface contaminants such as organic materials, metals, particles, andthe like, by a conducting cleaning process. It should be noted that sucha conventional cleaning process includes a final cleaning process thatuses a diluted hydrofluoric acid or hydrogenated water for terminatingthe dangling bonds exiting on the silicon surface by hydrogen. Thereby,formation of native oxide film on the silicon surface is suppressed, andthe silicon substrate thus having a cleaned surface is forwarded to thefollowing process of thermal oxidation. In the thermal oxidationprocess, the terminating hydrogen at the surface undergoes decouplingduring the process of raising the temperature of the silicon substratein an inert gas atmosphere such as argon (Ar) gas atmosphere. Oxidationof the silicon surface is conducted thereafter at the temperature ofabout 800° C. or more in the atmosphere in which oxygen molecules orwater molecules are introduced.

In the conventional thermal oxidation process, satisfactoryoxide/silicon interface characteristics, oxide breakdowncharacteristics, leakage current characteristics, and the like, areachieved only in the case a silicon surface having the (100) orientationis used for the formation of the silicon oxide film. Further, it isknown that there arises a remarkable deterioration of leakagecharacteristic in the case the thickness of the silicon oxide film thusformed by the conventional thermal oxidation process is reduced to about2 nm or less. Thus, it has been difficult to realize a high-performanceminiaturized transistor that requires decrease of the gate insulationfilm thickness.

Further, in the case the silicon oxide film is formed on a siliconcrystal having a surface orientation other than the (100) orientation oron a polysilicon formed on an insulation film, there arises a problem offormation of large interface state density at the oxide/siliconinterface as compared with the case the silicon oxide film is formed onthe (100)-oriented silicon surface, and this holds true even when thesilicon oxide film is formed by the thermal oxidation technology. Itshould be noted that a polysilicon film formed on an insulation film hasa primarily (111) oriented surface. Thus, such a silicon oxide film haspoor electric properties in terms of breakdown characteristics, leakagecurrent characteristics, and the like, particularly when the thicknessthereof is reduced, and there has been a need of increasing the filmthickness of the silicon oxide film when using such a silicon oxidefilm.

Meanwhile, the use of large-diameter silicon wafer substrate orlarge-area glass substrate is increasing these days for improving theefficiency of semiconductor device production. In order to formtransistors on the entire surface of such a large-size substrate withuniform characteristics and with high throughput, it is necessary toform the insulation film at a low temperature so as to decrease themagnitude of the temperature change, which takes place at the time ofthe heating process or at the time of the cooling process. Further, theprocess of forming such an insulation film is required to have smalltemperature dependence. In the conventional thermal oxidation process,it should be noted that there has been a large fluctuation of oxidationreaction rate caused by temperature fluctuation, and it has beendifficult to conduct the production process of semiconductor deviceswith high throughput while using a large-area substrate.

In order to solve these problems associated with the conventionalthermal oxidation technology, various low-temperature film formationprocesses have been attempted. Among others, the technology disclosed inJapanese Laid-Open Patent Publication 11-279773 or the technologydisclosed in Technical Digest of International Electron Devices Meeting,1999, pp. 249-252, or in 2000 Symposium on VLSI Technology Digest ofTechnical Papers, pp. 76-177, achieves relatively good electronicproperties for the film by conducting the oxidation of the siliconsurface by using atomic state oxygen O*. There, an inert gas having alarge metastable level is used for the atomization of the oxygenmolecules, and for this, the inert gas is introduced into plasmatogether with gaseous oxygen molecules.

In these technologies, it should be noted that a microwave is irradiatedto the mixed gas formed of an inert krypton (Kr) gas and an oxygen (O₂)gas, and a large amount of atomic state oxygen O* are formed. Thereby,the oxidation of silicon is conducted at a temperature of about 400° C.,and the properties comparable to those of the conventional thermaloxidation process, such as low leakage current characteristics, lowinterface state density high breakdown voltage, and the like, areachieved. Further, according to this oxidation technology, ahigh-quality oxide film is obtained also on the silicon surface having asurface orientation other than the (100) surface.

On the other hand, such a conventional silicon oxide film formationtechnology, even when using the microwave plasma, could at best realizea silicon oxide film having electric properties comparable to those ofthe film formed by the conventional thermal oxidation process, whichuses oxygen molecules or water molecules. Particularly, it has been notpossible to obtain the desired low leakage current characteristics inthe case the silicon oxide film has a thickness of about 2 nm or less onthe silicon substrate surface. Thus, it has been difficult to realizehigh-performance, miniaturized transistors that require further decreaseof the gate insulation film thickness, similarly to the case ofconventional thermal oxide film formation technology.

Further, there has been a problem that the silicon oxide film thusformed shows severe degradation of electric properties in the case thesilicon oxide film is used for a transistor, such as degradation ofconductance caused by hot carrier injection or increase of leakagecurrent in the case the silicon oxide film is used in a device such as aflash memory, which relies upon tunneling of electrons caused throughthe silicon oxide film, as compared with the case of using a siliconoxide film formed by the conventional thermal processes.

FIG. 1 shows the schematic structure of a conventional flash memorydevice 10.

Referring to FIG. 1, the flash memory device 10 is formed on a siliconsubstrate 11 doped to p-type or n-type and there is formed a floatinggate electrode 13 on the silicon substrate 11 via a tunneling oxide film12. The floating gate electrode 13 is covered with an inter-electrodeinsulation film 14, and a control gate electrode 15 is formed on thefloating gate electrode 13 via the inter-electrode insulation film 14.Further, a source region 11B and a drain region 11C of n-type or p-typeare formed in the silicon substrate 11 at both lateral sides of achannel region 11A right underneath the floating gate electrode 13.

In the flash memory device 10 of FIG. 1, the control gate electrode 15causes capacitance coupling with the floating gate electrode via theinter-electrode insulation film 14, and as a result, the potential ofthe floating gate electrode is controlled by the control voltage appliedto the control gate electrode 15.

Thus, in the case information is written into the floating gateelectrode in the flash memory device 10 of FIG. 1, a predetermined drivevoltage is applied across the drain region 11C and the source region 11Band a predetermined positive write voltage is applied to the controlgate electrode 15. Thereby, there are formed hot electrons as a resultof acceleration in the vicinity of the drain region 11C, and the hotelectrons thus formed are injected into the floating gate electrode 13via the tunneling oxide film 12.

In the case the information thus written is to be erased, apredetermined erase voltage is applied to the silicon substrate 11 or tothe source region 11B, and the electrons in the floating gate electrode13 are pulled out. In the case of reading the written information, apredetermined read voltage is applied to the control gate electrode 15and the electron current flowing through the channel region 11A from thesource region 11B to the drain region 11C is detected.

FIG. 2A shows the band structure of the flash memory 10 of FIG. 1 in thecross-sectional view that includes the floating gate electrode 13, thetunneling oxide film 12 and the silicon substrate 11, wherein FIG. 2Ashows the state in which no control voltage is applied to the controlgate electrode 15.

Referring to FIG. 2A, the tunneling insulation film 12 forms a potentialbarrier and it can be seen that the injection of the electrons on theconduction band Ec of the silicon substrate 11 into the floating gateelectrode 13 is effectively blocked.

FIG. 2B shows the band structure for the case a write voltage is appliedto the control gate electrode 15.

Referring to FIG. 2B, there is induced modification of the bandstructure in the tunneling insulation film 12 as a result of applicationof the write voltage, and as a result, the conduction band Ec forms atriangular potential. Thus, the hot electrons thus formed in the channelregion A are injected into the floating gate electrode 13 after passingthrough the triangular potential barrier in the form of Fowler-Nordheimtunneling current.

Now, in order to increase the writing speed in the flash memory device10, there is a need of increasing the tunneling probability of thetunneling current passing through the triangular potential in the stateof FIG. 2B. This can be achieved by decreasing the thickness of thetunneling oxide film 12. In the case the thickness of the tunnelingoxide film 12 is decreased, on the other hand, the electrons in thechannel may pass through the tunneling oxide film 12 in the non-writingstate shown in FIG. 2B by causing tunneling and form a leakage current.

FIG. 3 shows the relationship between the electric field applied to thetunneling oxide film 12 and the current density of the tunneling currentpassing through the tunneling oxide film 12.

Referring to FIG. 3, it is required that a tunneling current of about 1A/cm² can flow through the tunneling oxide film 12 in response to anelectric field of about 10 MV/cm applied to the tunneling oxide film 12in the writing state of FIG. 2B when to realize the writing time of1-10μ seconds in the flash memory device 10. In the case of non-writingstate of FIG. 2A, on the other hand, it is required that the leakagecurrent through the tunneling oxide film 12 be suppressed to 10⁻¹⁵ A/cm²or less at the application electric filed of 1 MV/cm². Thus, theconventional flash memory device 10 realizes the electric field—currentcharacteristic shown in FIG. 3 by a straight line by using a thermaloxide film having a thickness of several nanometers for the tunnelingoxide film 12.

On the other hand, when an attempt is made to reduce the thickness ofthe tunneling oxide film 12 for reducing the write time, the electricfield-current characteristic of the tunneling oxide film 12 is changedas represented in FIG. 3 by a curved line. There, it can be seen that,while there is caused a large increase of the tunneling current in thecase the electric field of 10 MV/cm is applied, and while theconventional tunneling current density of 1 A/cm² is realized in thestate of low electric field, there is caused a large increase in theleakage current in the non-writing state, and thus, the informationwritten into the floating gate electrode 13 is no longer retained.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful semiconductor device and fabrication process thereofwherein the foregoing problems are eliminated.

Another object of the present invention is to provide a dielectric filmshowing a small leakage current and is capable of providing a tunnelingcurrent of large current density at the time of application of anelectric field, as well as a formation method thereof.

Another object of the present invention is to provide a semiconductordevice or a non-volatile semiconductor device that uses such adielectric film and a fabrication method of such a semiconductor device.

Another object of the present invention is to provide a dielectric filmformed on a silicon surface,

said dielectric film containing nitrogen with a concentrationdistribution such that a nitrogen concentration increases at adielectric film surface as compared to a central part of the dielectricfilm.

Another object of the present invention is to provide a semiconductordevice, comprising:

a silicon substrate;

an insulation film formed on said silicon substrate; and

an electrode formed on said insulation film,

wherein said insulation film has a nitrogen concentration distributionsuch that a nitrogen concentration increases at a film surfacecontacting with said electrode as compared with a central part of saidfilm.

Another object of the present invention is to provide a non-volatilesemiconductor memory device, comprising:

a silicon substrate;

a tunneling insulation film formed on said silicon substrate;

a floating gate electrode formed on said tunneling insulation film; and

a control gate electrode formed on said floating gate electrode via aninter-electrode insulation film,

one of said insulation films having a nitrogen concentrationdistribution such that a nitrogen concentration increases at the filmsurface contacting with said electrode as compared with a central partof said film.

Another object of the present invention is to provide a method offorming a dielectric film, comprising the steps of:

forming a silicon oxide film on a surface;

modifying a surface of said silicon oxide film by exposing the same tohydrogen nitride radicals NH*.

Another object of the present invention is to provide a method offorming a dielectric film, comprising the steps of:

forming a silicon oxide film on a surface; and

modifying a surface of said silicon oxide film by exposing the same tomicrowave plasma formed in a mixed gas of an inert gas selected from Aror Kr and a gas containing nitrogen and hydrogen as constituentelements.

Another object of the present invention is to provide a method offorming a dielectric film comprising the step of exposing a siliconsurface to microwave plasma formed in a mixed gas of an inert gasprimarily formed of Kr, a gas containing nitrogen as a constituentelement and a gas containing oxygen as a constituent element, to form anoxynitride film on said silicon surface.

Another object of the present invention is to provide a method offabricating a semiconductor device, comprising the steps of;

forming a silicon oxide film on a silicon substrate by an oxidationprocessing;

modifying a surface of said silicon oxide film by exposing the same tohydrogen nitride radicals NH*; and

forming a gate electrode on said modified silicon oxide film.

Another object of the present invention is to provide a method offabricating a semiconductor device, comprising the steps of:

forming a silicon oxide film on a silicon substrate by an oxidationprocessing;

modifying a surface of said silicon oxide film by exposing the same tomicrowave plasma formed in a mixed gas of an inert gas selected from Aror Kr and a gas containing nitrogen and hydrogen as constituentelements; and

forming a gate electrode on said modified silicon oxide film.

Another object of the present invention is to provide a fabricationmethod of a semiconductor device, comprising the steps of:

exposing a silicon substrate surface to microwave plasma formed in amixed gas of an inert gas primarily formed of Kr, a gas containingnitrogen as a constituent element and a gas containing oxygen as aconstituent element, to form an oxynitride film on said silicon surface;and

forming a gate electrode on said oxynitride film.

According to the present invention, the surface of the oxide film ismodified by exposing the surface of the oxide film formed on a surfaceof a silicon substrate or the like to microwave plasma formed in a mixedgas of an inert gas primarily formed of Ar or Kr and a gas containingnitrogen and hydrogen, and nitrogen are concentrated to a surface regionof the oxide film within the depth of several nanometers. Nitrogen thusconcentrated to the oxide film surface form a substantially layerednitride region on the oxide film surface, and as a result, the oxidefilm is changed to a structure approximately similar to the one in whicha nitride film is laminated on the surface of the silicon oxide film.

In the dielectric film having such a structure, there is provided aregion of small bandgap in correspondence to the nitride region adjacentto a region of large bandgap corresponding to the silicon oxide filmregion, and because of the fact that the nitride region has a specificdielectric constant larger than that of the silicon oxide film, thedielectric film structure shows an effectively large film thickness withregard to the electrons in the channel region 11A in the state that nocontrol voltage is applied to the control gate electrode 15, and thetunneling of the electrons is effectively blocked.

In the case a write voltage is applied to the control gate electrode 15,on the other hand, the band structures of the oxide film region and thenitride region constituting the dielectric film structure are changed.Thereby, the effective thickness of eth oxide film region is reducedwith the formation of the nitride region, and as a result, the hotelectrons in the channel region 11A are allowed to cause tunnelingthrough the dielectric film structure efficiently. Because the nitrideregion formed on the surface of the oxide film region has a smallbandgap, it does not function as a potential barrier to the hotelectrons to be injected.

As a result of using such a dielectric film structure for the tunnelinginsulation film of the non-volatile semiconductor memory device such asa flash memory, and the like, it becomes possible to increase the wiringspeed or reduce the operational voltage while simultaneously reducingthe leakage current.

It should be noted that such an oxide film, in which there is causednitrogen concentration at the surface part thereof, can be formed alsoby exposing the silicon surface to microwave plasma formed in a mixedgas of an inert gas primarily formed of Kr, a gas containing nitrogen asa constituent element and a gas containing oxygen as a constituentelement. The oxide film thus formed has the composition of an oxynitridefilm as a whole, while it should be noted that a part of nitrogen areconcentrated in such a structure to the interface between the oxynitridefilm and the silicon surface for relaxing the stress, while othernitrogen are concentrated to the film surface and form the desirednitride layer region. In the oxynitride film of such a structure, thereis caused stress relaxation by the nitrogen concentrated to theinterface to the silicon substrate, and because of this, the density ofthe electric charges trapped in the film or the density of the interfacestates is reduced and the leakage current path other than the tunnelingmechanism is effectively blocked. Thus, the oxynitride film obtainedaccording to such a process has an extremely high film quality. In suchan oxynitride film, it is preferable that the hydrogen concentrationcontained in the film is 10¹² cm⁻² or less, preferably 10¹¹ cm⁻² or lessin terms of surface density.

As the formation of the dielectric film can be conducted at a lowtemperature of 550° C. or less in the present invention, it is possibleto recover the oxygen defects in the film without decoupling thehydrogen terminating the dangling bonds in the oxide film. This appliedalso to the formation of the nitride film or oxynitride film to beexplained later.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a conventional flashmemory device;

FIGS. 2A and 2B are diagrams explaining the operation of the flashmemory device;

FIG. 3 is a diagram explaining the problems of the conventional flashmemory device;

FIGS. 4A-4C are diagrams showing the formation process of an oxide filmand the fabrication process of a semiconductor device according to afirst embodiment of the present invention;

FIG. 5 is a diagram showing the schematic construction of a plasmaapparatus having a radial line slot antenna and used in the presentinvention;

FIG. 6 is a characteristic diagram showing the exposure effect of thebond formed between the surface-terminating hydrogen at the siliconsurface and silicon caused by exposure to Kr plasma as obtained byinfrared spectroscopy;

FIG. 7 is a characteristic diagram showing the dependence of siliconoxide film thickness on the gas pressure of the processing chamber;

FIG. 8 is a characteristic diagram showing the depth distributionprofile of the Kr density ion the silicon oxide film;

FIG. 9 is a characteristic diagram showing the current versus voltagecharacteristic of the silicon oxide film;

FIG. 10 is a diagram showing the relationship between the leakagecurrent of the silicon oxide film and the silicon oxynitride film andthe film thickness;

FIGS. 11A-11C are diagrams showing the formation method of a nitridefilm and a fabrication method of a semiconductor device according to asecond embodiment of the present invention;

FIG. 12 is a characteristic diagram showing the dependence of thesilicon nitride film thickness on the gas pressure of the processingchamber;

FIGS. 13A-13D are diagrams showing the formation method of anoxide/nitride laminated dielectric film and a fabrication method of asemiconductor device according to a third embodiment of the presentinvention;

FIG. 14 is a diagram showing the nitrogen distribution in theoxide/nitride laminated dielectric film;

FIG. 15 is a band structure diagram of the oxide/nitride laminateddielectric film;

FIGS. 16A-16C are diagrams showing the formation method of an oxynitridefilm and a fabrication method of a semiconductor device according to afourth embodiment of the present invention;

FIG. 17 is a diagram showing the photoemission intensity of atomic stateoxygen and atomic state hydrogen at the time of formation of theoxynitride film;

FIG. 18 is a diagram showing the elemental distribution profile in thesilicon oxynitride film;

FIG. 19 is a characteristic diagram showing the current versus voltagecharacteristic of the silicon oxynitride film;

FIG. 20 is a schematic diagram showing the time-dependent change ofnitrogen in the silicon nitride film;

FIGS. 21A-21C are schematic diagrams showing the shallow trenchisolation according to a fifth embodiment of the present invention;

FIG. 22 is a cross-sectional diagram of a three-dimensional transistorformed on a silicon surface having projections and depressions accordingto the fifth embodiment of the present invention;

FIG. 23 is a diagram showing the construction of a flash memory deviceaccording to a sixth embodiment of the present invention;

FIG. 24 is a band structure diagram showing the writing operation of theflash memory device of FIG. 23;

FIG. 25 is a diagram showing the leakage current characteristics of thetunneling insulation film in the flash memory device of FIG. 23;

FIG. 26 is a schematic diagram showing the cross-sectional structure ofa flash memory device according to a seventh embodiment of the presentinvention;

FIGS. 27-30 are schematic cross-sectional diagrams showing thefabrication process of the flash memory device of FIG. 26 step by step;

FIG. 31 is a schematic diagram showing the cross-sectional structure ofa MOS transistor formed on a metal substrate SOI according to an eighthembodiment of the present invention;

FIG. 32 is a schematic diagram of a plasma processing apparatusaccording to a ninth embodiment of the present invention applicable to aglass substrate or plastic substrate;

FIG. 33 is a schematic diagram showing the cross-sectional structure ofa polysilicon transistor on an insulation film formed according to theplasma processing apparatus of FIG. 32; and

FIG. 34 is a schematic diagram showing the cross-sectional diagram of athree-dimensional LSI according to a tenth embodiment of the presentinvention.

BEST MODE FOR IMPLEMENTING THE INVENTION

Hereinafter, various preferable embodiments to which the presentinvention is applied will be explained in detail with reference to thedrawings.

FIRST EMBODIMENT

FIGS. 4A-4C show the low-temperature formation process of an oxide filmthat uses plasma as well as the fabrication process of a semiconductordevice that uses such an oxide film according to a first embodiment ofthe present invention. Further, FIG. 5 shows an example of a plasmaprocessing apparatus used in the present invention and having a radialline slot antenna in a cross-sectional view.

In the present embodiment, the hydrogen terminating the dangling bondsat a silicon surface is first removed in the step of FIG. 4A. Morespecifically, the removal process of the surface-terminating hydrogenand the oxidation process are conducted in the same processing chambercontinuously, and the Kr gas, which is used for the plasma excitationgas in the subsequent oxide film formation process, is used in theremoval process of the surface-terminating hydrogen.

First, a vacuum vessel (processing chamber) 101 is evacuated in theplasma processing apparatus of FIG. 5 and an Ar gas is introduced firstfrom a shower plate 102. Then, the gas is changed to the Kr gas.Further, the pressure inside the processing chamber 101 is set to about133 Pa (1 Torr).

Next, a silicon substrate 103 is placed on a stage 104 having a heatingmechanism, and the temperature of the specimen is set to about 400° C.As long as the temperature of the silicon substrate 103 is in the rangeof 200-500° C., the same results explained as below are obtained. Itshould be noted that the silicon substrate 103 is subjected to atreatment in a diluted hydrofluoric acid in the preprocessing stepimmediately before, and as a result, the dangling bonds on the surfaceof the silicon substrate are terminated by hydrogen.

Next, a microwave of 2.45 GHz is supplied to a radial line slot antenna106 from a coaxial waveguide 105 with the frequency of 2.45 GHz, whereinthe microwave thus supplied is introduced into the processing chamber101 from the radial line slot antenna 106 through a dielectric plate 107provided on a part of the wall of the processing chamber 101. Themicrowave thus introduced cause excitation of the Kr gas introduced intothe processing chamber 101 from the shower plate 102, and as a result,there is induced high-density Kr plasma right underneath the showerplate 102. As long as the frequency of the microwave thus supplied is inthe range of about 900 MHz or more but not exceeding about 100 GHz,almost the same results explained as below are obtained.

In the construction of FIG. 5, the separation between the shower plate102 and the substrate 103 is set to 6 cm in the present embodiment.Smaller the gap separation, the film formation rate becomes faster.Further, while the present embodiment shows the example of filmformation by using the plasma apparatus that uses a radial line slotantenna, it should be noted that the plasma may be induced byintroducing the microwave into the processing chamber by other ways.

By exposing the silicon substrate 103 to the plasma thus excited by theKr gas, the surface of the silicon substrate 103 experiences bombardmentof low energy Kr ions, and as a result, the surface-terminating hydrogenare removed.

FIG. 6 shows the result of analysis of the silicon-hydrogen bond on thesurface of the silicon substrate 103 by means of infrared spectrometerand shows the effect of removal of the surface-terminating hydrogen atthe silicon surface by the Kr plasma induced by introducing themicrowave into the processing chamber 101 under the pressure of 133 Pa(1 Torr) with the power of 1.2 W/cm².

Referring to FIG. 6, it can be seen that the optical absorption at about2100 cm⁻¹, which is characteristic to the silicon-hydrogen bond, is moreor less vanished after the Kr plasma radiation conducted for only 1second. Further, after continuous irradiation for thirty seconds, thisoptical absorption is almost completely vanished. This means thesurface-terminating hydrogen on the silicon surface can be removed bythe Kr plasma irradiation conducted for about 30 seconds. In the presentembodiment, the surface-terminating hydrogen is completely removed byconducting the Kr plasma irradiation for 1 minute.

Next, in the step of FIG. 4B, a Kr/O₂mixed gas is introduced from theshower plate 102 with a partial pressure ratio of 97/3. Thereby, thepressure of the processing chamber is maintained at about 133 Pa (1Torr). In the high-density excitation plasma in which the Kr gas and theO₂ gas are mixed, Kr* in the intermediate excitation state and the O₂molecules cause collision and there is caused efficient formation ofatomic state oxygen O* in large amount.

In the present embodiment, the atomic state oxygen O* thus formed areused for oxidizing the surface of the silicon substrate 103, and as aresult, there is formed an oxide film 103A. In the thermal oxidationprocess conducted conventionally on a silicon surface, the oxidation iscaused by the O2 molecules or H₂O molecules and a very high temperatureof 800° C. or more has been needed. In the oxidation processing of thepresent invention conducted by the atomic state oxygen O*, the oxidationbecomes possible at a very low temperature of about 400° C. In order tofacilitate the collision of Kr* and O₂, it is preferable to use a highpressure for the pressure of the processing chamber. However, the use ofexcessively high pressure facilitates mutual collision of O* thusformed, and the atomic state oxygen O* thus formed are returned to theO₂molecules. Thus, there exists an optimum gas pressure.

FIG. 7 shows the relationship between the thicknesses of the oxide film103A thus formed and the internal pressure of the processing chamber forthe case the pressure inside the processing chamber 101 is changed whilemaintaining the Kr/O₂ pressure ratio to 97/3. In FIG. 7, the temperatureof the silicon substrate 103 is set to 400° C. and the oxidationprocessing is conducted for 10 minutes.

Referring to FIG. 7, it can be seen that the oxidation rate becomesmaximum in the case the pressure inside the processing chamber 101 isabout 133 Pa (1 Torr) and that this pressure or the pressure conditionnear this is the optimum condition. This optimum pressure is not limitedto the case in which the silicon substrate 103 has the (100) surfaceorientation but is valid also in other cases in which the siliconsurface has any other surface orientations.

After the silicon oxide film 103A is thus formed to the desired filmthickness, the introduction of the microwave power is shutdown and theplasma excitation is terminated. Further, the Kr/O₂ mixed gas isreplaced with the Ar gas, and with this, the oxidation processing isterminated. It should be noted that the use of the Ar gas before andafter the foregoing step is intended to enable the use of low-cost Argas cheaper than Kr for the purging gas. The Kr gas used in the presentstep is recovered and reused.

Following the foregoing oxide film formation process, the gate electrode103B is formed on the oxide film 103A, and a semiconductor integratedcircuit device including transistors and capacitors is formed afterconducting various patterning processing, ion implantation processing,passivation film formation processing, hydrogen sintering processing,and the like.

The result of measurement of hydrogen content in the silicon oxide filmformed according to the foregoing process indicates that the hydrogencontent is about 10²²/cm² or less in terms of surface density in thecase the silicon oxide film has a thickness of 3 nm, wherein it shouldbe noted that the foregoing measurement was conducted by measuring thehydrogen release caused with temperature rise. Particularly, it wasconfirmed that the oxide film characterized by a small leakage currentshows that the hydrogen content in the silicon oxide film is about10¹¹/cm² or less in terms of surface density. On the other hand, theoxide film not exposed to the Kr plasma before the oxide film formationcontained hydrogen with the surface density exceeding 10¹²/cm².

Further, the comparison was made on the roughness of the silicon surfacebefore and after the oxide film formation conducted according to theprocess noted before wherein the measurement of the surface roughnesswas made by using an atomic force microscope. It should be noted thatthe silicon surface was exposed after the oxide film formation, byremoving the silicon oxide film thus formed. It was confirmed that thereis caused no change of surface roughness. Thus, there is caused noroughening of silicon surface even when the oxidation processing isconducted after the removal of the surface-terminating hydrogen.

FIG. 8 shows the depth profile of Kr density in the silicon oxide filmformed according to the foregoing process as measured by the totalreflection X-ray fluorescent spectrometer. It should be noted that FIG.7 shows the result for the silicon (100) surface, while this result isnot limited to the (100) surface and a similar result is obtained alsoin other surface orientations.

In the experiment of FIG. 8, the partial pressure of oxygen in Kr is setto 3% and the pressure of the processing chamber is set to 133 Pa (133Torr). Further, the plasma oxidation processing is conducted at thesubstrate temperature of 400° C.

Referring to FIG. 8, the Kr density in the silicon oxide film increaseswith increasing distance from the silicon surface and reaches the valueof about 2×10¹¹/cm² at the surface of the silicon oxide film. Thisindicates that the silicon oxide film obtained according to theforegoing processing is a film in which the Kr concentration is constantin the film in the region in which the distance to the underlyingsilicon surface is 4 nm or more and in which the Kr concentrationdecreases toward the silicon/silicon oxide interface in the regionwithin the distance of 4 nm from the silicon surface.

FIG. 9 shows the dependence of the leakage current on the appliedelectric field for the silicon oxide film obtained according to theforegoing process. It should be noted that the result of FIG. 9 is forthe case in which the thickness of the silicon oxide film is 4.4 nm. Forthe purpose of comparison, FIG. 9 also shows the leakage currentcharacteristic in which no exposure to the Kr plasma was conductedbefore the formation of the oxide film.

Referring to FIG. 9, the leakage current characteristic of the siliconoxide film not exposed to the Kr plasma is equivalent to the leakagecurrent characteristic of the conventional thermal oxide film. Thismeans that the Kr/O₂ microwave plasma processing does not improve theleakage current characteristics of the oxide film thus obtained verymuch. On the other hand, in the case the oxidation processing isconducted by the present embodiment in which the Kr/O₂ gas is introducedafter the Kr plasma irradiation processing, it can be seen that theleakage current is improved by the order of 2 or 3 as compared with theleakage current of the silicon oxide film formed by the conventionalmicrowave plasma oxidation processing when measured at the same electricfield, indicating that the silicon oxide film formed by the presentembodiment has excellent low leakage characteristics. It is furtherconfirmed that a similar improvement of leakage current characteristicis achieved also in the silicon oxide film having a much thinner filmthickness of 1.7 nm.

FIG. 10 shows the result of measurement of the leakage currentcharacteristics of the silicon oxide film of the present embodiment forthe case the thickness of the silicon oxide film is changed variously.In FIG. 10, Δ shows the leakage current characteristic of a conventionalthermal oxide film, ∘ shows the leakage current characteristic of thesilicon oxide film formed by conducting the oxidation processing by theKr/O2plasma while omitting the exposure process to the Kr plasma, while

shows the leakage current characteristic of the silicon oxide film ofthe present embodiment in which the oxidation is conducted by the Kr/O₂plasma after exposure to the Kr plasma. In FIG. 9, it should be notedthat the data represented by

shows the leakage current characteristic of an oxynitride film to beexplained later.

Referring to FIG. 10, it can be seen that the leakage currentcharacteristic of the silicon oxide film represented by ∘ and formed bythe plasma oxidation processing while omitting the exposure process tothe Kr plasma coincides with the leakage current characteristic of thethermal oxide film represented by Δ, while it can be seen also that theleakage current characteristics of the silicon oxide film of the presentembodiment and represented by

is reduced with respect to the leakage current characteristicsrepresented by ∘ by the order of 2-3. Further, it can be seen that aleakage current of 1×10⁻² A/cm², which is comparable to the leakagecurrent of the thermal oxide film having the thickness of 2 nm, isachieved in the silicon oxide film of the present embodiment in the casethe oxide film has the thickness of about 1.5 nm.

Further, the measurement of the surface orientation dependence conductedon the silicon/silicon oxide interface state density for the siliconoxide film obtained by the embodiment of the present invention hasrevealed the fact that a very low interface state density of about1×10¹⁰ cm⁻²eV⁻¹ is obtained for any silicon surface of any surfaceorientation.

Further, the oxide film formed by the present embodiment showsequivalent or superior characteristics as compared with the conventionalthermal oxide film with regard to various electric and reliabilitycharacteristics such as breakdown characteristics, hot carrierresistance, charge-to-breakdown electric charges QBD, which correspondsto the electric charges up to the failure of the silicon oxide filmunder a stress current, and the like.

As noted above, it is possible to form a silicon oxide film on a siliconsurface of any surface orientation at a low temperature of 400° C. byconducting the silicon oxidation processing by the Kr/O₂ high-densityplasma after removal of the terminating hydrogen. It thought that suchan effect is achieved because of the reduced hydrogen content in theoxide film caused as a result of the removal of the terminating hydrogenand because of the fact that the oxide film contains Kr. Because of thereduced amount of hydrogen in the oxide film, it is believed that weakelement bonding is reduced in the silicon oxide film. Further, becauseof the incorporation of Kr in the film, the stress inside the film andparticularly at the Si/SiO₂ interface is relaxed, and there is caused areduction of trapped electric charges or reduction of interface statedensity. As a result, the silicon oxide film shows significantlyimproved electric properties.

Particularly, it is believed that the feature of reducing the hydrogenconcentration in the film to the level of 10¹²/cm² or less, preferablyto the level of 10¹¹ cm² or less, and the feature of incorporation of Krinto the film with a concentration of 5×10¹¹/cm² or less are thought ascontributing to the improvement of electric properties and reliabilityof the silicon oxide film.

In order to realize the oxide film of the present invention, it is alsopossible to use a plasma processing apparatus other than the one shownin FIG. 5, as long as the plasma processing apparatus can conduct theoxide film formation at low temperatures by using plasma. For example,it is possible to use a two-stage shower plate-type plasma processingapparatus in which there are provided a first gas release structure forreleasing Kr for plasma excitation by a microwave and a second gasrelease structure different from the first gas release structure forreleasing the oxygen gas.

In the present embodiment, it should be noted that the feeding of themicrowave power is shutdown upon formation of the silicon oxide film toa desired film thickness, followed by the process of replacing the Kr/O₂mixed gas with the Ar gas. On the other hand, it is also possible tointroduce a Kr/NH₃ mixed gas from the shower plate 102 with the partialpressure ratio of 98/2 before shutting down the microwave power whilemaintaining the pressure at about 133 Pa (1 Torr). Thereby, a siliconnitride film of about 0.7 nm thickness is formed on the surface of thesilicon oxide film upon termination of the processing. According to sucha process, it becomes possible to form an insulation film having ahigher specific dielectric constant by forming a silicon oxynitride filmin which a silicon nitride film is formed on the surface thereof.

SECOND EMBODIMENT

FIGS. 11A-11C show the formation method of a nitride film at lowtemperature by using plasma according to a second embodiment of thepresent invention, as well as the fabrication method of a semiconductordevice that uses such a nitride film.

In the present embodiment, too, an apparatus similar to the one shown inFIG. 5 is used for the nitride film formation. Further, in the presentembodiment, it is preferable to use Ar or Kr for the plasma excitationgas for removing the terminating hydrogen and for the nitride filmformation, in order to form a high-quality nitride film.

Hereinafter, an example of using Ar will be represented.

First, the interior of the vacuum vessel (processing chamber) 101 ofFIG. 5 is evacuated to a vacuum state in the step of FIG. 11A and an Argas is introduced from the shower plate 102 such that the pressureinside the processing chamber is set to about 13.3 Pa (100 mTorr).

Next, a silicon substrate 103 is introduced into the processing chamber101 and is placed on the state 104 in which there is provided a heatingmechanism, wherein the silicon substrate is subjected to a cleaningprocess conducted in a hydrogenated water and the silicon dangling bondsat the substrate surface are terminated by hydrogen. Further, thetemperature of the specimen is set to 500° C. As long as the temperatureis in the range of 300-550° C., results similar to the one describedbelow are obtained.

Next, a microwave of 2.45 GHz is supplied into the processing chamberfrom the coaxial waveguide 105 via the radial line slot antenna 106 andthe dielectric plate 107 and a high-density plasma of Ar is induced inthe processing chamber. As long as the frequency of the suppliedmicrowave is in the range of about 900 MHz or more but not exceedingabout 10 GHz, results similar to the one described below are obtained.In the present embodiment, the separation between the shower plate 102and the substrate 103 is set to 6 cm. With decreasing separation, fasterdeposition rate becomes possible.

While the present embodiment shows the example of film formation by aplasma apparatus that uses the radial line slot antenna, it is alsopossible to introduce the microwave into the processing chamber by othermethods.

The silicon surface thus exposed to the plasma excited based on an Argas is subjected to bombardment of low energy Ar ions, and thesurface-terminating hydrogen are removed as a result. In the presentembodiment, the Ar plasma exposure process is conducted for 1 minute.

Next, in the step of FIG. 11B, an NH₃ gas is mixed to the Ar gas fromthe shower plate 102 with a partial pressure ratio of 2%. Thereby, thepressure of the processing chamber is held at about 13.3 Pa (100 mTorr).In high-density plasma in which the Ar gas and the NH₃ gas are mixed,there are caused collision of Ar* in the intermediate excited state andthe NH₃ molecules, and NH* radicals are formed efficiently. The NH*radicals thus formed cause nitridation of the silicon substrate surface,and as a result, there is formed a silicon nitride film 103 on thesurface of the silicon substrate 103.

Upon formation of the silicon nitride film 103C with a predeterminedthickness, the supply of the microwave power is shutdown and theexcitation of the plasma is terminated. Finally, the Ar/NH₃ mixed gas isreplaced with the Ar gas and the nitridation processing is terminated.

Further, in the step of FIG. 11C, the silicon nitride film 103C thusformed by the nitride film formation process in the step of FIG. 11C isused as a gate insulation film and the gate electrode 103D is formed onthe gate insulation film 103C. Further, various patterning processes,ion implantation processes, passivation film formation processes,hydrogen sintering processes, and the like are conducted, and asemiconductor integrated circuit that includes therein transistors andcapacitors is obtained.

While the present embodiment showed the case in which the nitride filmis formed by the plasma processing apparatus that uses the radial lineslot antenna, it is also possible to introduce the microwave into theprocessing chamber by other ways. Further, while the present embodimentuses Ar for the plasma excitation gas, similar results are obtained alsowhen Kr is used. Further, while the present embodiment uses NH₃ for theprocess gas, it is also possible to use a mixed gas of N₂ and H₂ forthis purpose.

In the silicon nitride film formation process of the present invention,it is important that there remains hydrogen in the plasma even after thesurface-terminating hydrogen are removed. As a result of existence ofhydrogen in the plasma, the dangling bonds inside the silicon nitridefilm as well as the dangling bond on the interface are terminated byforming Si—H bonds or N—H bond, and a result, electron traps areeliminated from the silicon nitride film and the interface.

The existence of the Si—H bond and the N—H bond is confirmedrespectively by infrared absorption spectroscopy and by X-rayphotoelectron spectroscopy. As a result of existence of hydrogen, thehysteresis in the CV characteristics is eliminated and the interfacestate density at the silicon/silicon nitride film is suppressed to2×10¹⁰ cm⁻². In the case of forming the silicon nitride film by using arare gas (Ar or Kr) and an N₂/H₂ mixed gas, it is possible to suppressthe traps of electrons or holes in the film drastically by setting thepartial pressure of the hydrogen gas to 0.5% or more.

FIG. 12 shows the pressure dependence of the silicon nitride filmthickness formed according to the process noted above. In the experimentof FIG. 12, it should be noted that the Ar/NH₃ partial pressure ratiowas set to 98/2 and the deposition was conducted for 30 minutes.

Referring to FIG. 12, it can be seen that there occurs an increase ofdeposition rate of the nitride film by reducing the pressure in theprocessing chamber and thus by increasing the energy given to NH₃ (orN₂/H₂). Thus, from the viewpoint of efficiency of nitride filmformation, it is preferable to set the gas pressure to the range of6.65-13.3 Pa (50-100 mTorr). On the other hand, from the viewpoint ofproductivity, it is preferable to use a unified pressure suitable to theoxidation processing such as 133 Pa (1 Torr), particularly in the caseof conducting the oxidation processing and the nitridation processingcontinuously, as will be explained with reference to other embodiments.Further, it is preferable to set the partial pressure of NH₃ (or N₂/H₂)in the rare gas to the range of 1-10%, more preferably to the range of2-6%.

It should be noted that the silicon nitride film 103C thus obtained bythe present embodiment showed the specific dielectric constant of 7.9,while this value is about twice as large as the specific dielectricconstant of a silicon oxide film.

Measurement of the current versus voltage characteristics of the siliconnitride film 103C obtained by the present embodiment has revealed thefact that the film shows a leakage current characteristic smaller by theorder of 5-6 than that of a thermal oxide film having the thickness of1.5 nm in the case the film has a thickness of 3.0 nm (equivalent to theoxide film thickness of 1.5 nm), under the condition that a voltage of 1V is applied. This means that it is possible to break through thelimitation of miniaturization that appears in the conventionaltransistors that use a silicon oxide film for the gate insulation film,by using the silicon nitride film of the present embodiment.

Further, it should be noted that the film formation condition of thenitride film noted above as well as the physical and electricalproperties are not limited to the case of forming the silicon nitridefilm on the (100) oriented silicon surface but are valid also in thecase of forming the silicon nitride film on the silicon of any surfaceorientation including the (111) surface.

It should be noted that the preferable results achieved by the presentembodiment are not only attained by the removal of the terminatinghydrogen but also by the existence of Ar or Kr in the nitride film.Thus, in the nitride film of the present embodiment, it is believed thatAr or Kr relaxes the stress inside the nitride film or at thesilicon/nitride film interface. As a result, the fixed electric chargesin the nitride film or the interface state density is reduced, and thiscontributed also to the remarkable improvement of the electricproperties and the reliability of the nitride film.

Particularly, it is thought that the existence of Ar or Kr with thesurface density of 5×1011/cm2 or less is effective for the improvementof the electric properties and reliability of the silicon nitride film,just like the case of the silicon oxide film.

In order to realize the nitride film 103C of the present invention, itis also possible to use other plasma processing apparatus than the oneshown in FIG. 5, as long as it enables low temperature oxide filmformation by using plasma. For example, it is possible to use atwo-stage shower plate type plasma processing apparatus that includes afirst gas release structure for releasing an Ar or Kr gas for excitationof plasma by microwave and a second gas release structure different fromthe first gas release structure for releasing the NH₃ (or N₂/H₂) gas.

THIRD EMBODIMENT

FIGS. 13A-13D show the formation method of a two-layer laminateddielectric structure according to a third embodiment of the presentinvention in which an oxide film and nitride film formed by thelow-temperature plasma process are laminated, as well as a fabricationprocess of a semiconductor device that uses such a two-layer laminateddielectric structure.

It should be noted that the apparatus used for the formation of theoxide film and the nitride film in the present embodiment is identicalwith the apparatus of FIG. 5. In the present embodiment, Kr is used forthe plasma excitation gas at the time of formation of the oxide film andthe nitride film.

First, in the step of FIG. 13A, the vacuum vessel (processing chamber)101 is evacuated to the vacuum state and an Ar gas is introduced intothe processing chamber 101 from the shower plate 102. Next, the gas tobe introduced the next is switched to the Kr gas from the initial Argas, and the pressure of the processing chamber 101 is set to about 133Pa (1 Torr).

Next, the silicon substrate 103, preprocessed in the preprocessing stepimmediately before by conducting the diluted hydrofluoric acid treatmentfor terminating the surface dangling bonds of silicon by hydrogen, isintroduced into the processing chamber 101 and placed on the stage 104having a heating mechanism. Further, the temperature of the specimen isset to 400° C.

Next, a microwave of 2.45 GHz frequency is introduced to the radial lineslot antenna 106 from the coaxial waveguide 105 for 1 minute, whereinthe microwave thus supplied is introduced into the processing chamber101 via the dielectric plate 107.

Thereby, there is induced high-density Kr plasma in the processingchamber 101, and the surface-terminating hydrogen is removed by exposingthe surface of the silicon substrate 103 to the plasma.

Next, in the step of FIG. 13B, the pressure inside the processingchamber 101 is maintained at 133 Pa (1 Torr) and a Kr/O2mixed gas isintroduced from the shower plate 102 with the partial pressure ratio of97/3. Thereby, there is formed a silicon oxide film 103A on the surfaceof the silicon substrate 103 with a thickness of 1.5 nm.

Next, in the step of FIG. 13C, the supply of the microwave is shutdownmomentarily and supply of the O₂ gas is terminated. After purging theinterior of the vacuum vessel (processing chamber) 101 with Kr, a mixedgas of Kr/NH₃ is introduced from the shower plate 103 with a partialpressure ratio of 98/2. Further, the pressure of the processing chamberis set to about 133 Pa (1 Torr) and the microwave of 2.56 GHz isintroduced again to form the high-density plasma in the processingchamber 101. With this, a silicon nitride film 103N is formed on thesurface of the silicon oxide film 103A with the thickness of 1 nm.

Upon formation of the silicon nitride film 103A with the desiredthickness, the microwave power is shutdown and the plasma excitation isterminated.

Further, the Kr/NH₃ mixed gas is replaced with the Ar gas and theoxynitridation processing is terminated.

Next, in the step of FIG. 13D, the oxynitride film thus obtained is usedfor the gate insulation film and a gate electrode 103B is formedthereon. Further, by conducting various patterning processing, ioninjection processing, passivation film formation processing, hydrogensintering processing, and the like, a semiconductor integrated circuithaving transistors or capacitors is obtained.

Measurement of the effective dielectric constant conducted on such alaminated gate insulation film has revealed the value of about 6.Further, the film showed excellent electric properties and reliabilitysuch as leakage current characteristic, breakdown characteristic,hot-carrier resistance, similarly to the case of the first embodiment.The gate insulation film thus obtained showed no dependence of surfaceorientation of the silicon substrate 103, and excellent gate insulationfilm was formed also on the silicon of any surface orientation otherthan the (100) surface.

While the present embodiment explained the two-layer construction inwhich an oxide film located closer to the silicon side and a nitridefilm are laminated, it is also possible to change the order oflamination of the oxide film and the nitride film depending on thepropose. Further, it is also possible to form the structure of plurallaminated films such as oxide/nitride oxide, nitride/oxide/nitride, andthe like.

FIG. 14 shows the nitrogen concentration distribution in the two-layerlaminated structure obtained by the present embodiment.

Referring to FIG. 14, it can be seen that there is caused concentrationof nitrogen in correspondence to the nitride film 103N at the depth of2-3 nm from the surface of the dielectric film, while there occurs nofurther penetration of nitrogen. Thus, according to the presentembodiment, it is possible to form a nitride region at the oxide filmsurface with the thickness of 2-3 nm stably.

FIG. 15 shows the band structure of the semiconductor device of FIG. 13Dtaken along the cross-section A-A′ for the thermal equilibrium state.

Referring to FIG. 15, there is formed a nitride layer 103N of smallbandgap adjacent to the silicon oxide layer 103A of large bandgap, andthe gate electrode 103B is formed adjacent to the nitride film layer103N. Further, the silicon substrate 103 exists adjacent to the siliconoxide film layer 103A.

In such a band structure, it should be noted that the conductionelectrons in the silicon substrate 103 are blocked by the thickdielectric film formed of the silicon oxide film 103A and the nitridefilm 103N as long as the semiconductor device is in the non-drivingstate in which no voltage is applied to the gate electrode 103A, andthere is caused no leakage of the conduction electrons tot eh gateelectrode 103A. As will be explained later with reference to the flashmemory device, the band structure of FIG. 15 is extremely effective forsuppressing, the leakage current and simultaneously increasing thecurrent density of the tunneling current.

FOURTH EMBODIMENT

FIG. 16A-16C show the formation method of an oxynitride film conductedat low temperature by using plasma according to a fourth embodiment ofthe present invention and a fabrication process of a semiconductordevice that uses such an oxynitride film. It should be noted that theoxynitride film formation apparatus used in the present embodiment isidentical with the one shown in FIG. 5. In the present embodiment, Kr isused for the plasma excitation gas.

First, the interior of the vacuum vessel (processing camber 101) of FIG.5 is evacuated to the vacuum state in the step of FIG. 16A, and an Argas is introduced into the processing chamber 101 from the shower plate102. Next, the gas introduced to the processing chamber 101 is switchedto a Kr gas from the Ar gas, and the pressure inside the processingchamber is set to about 133 Pa(1 Torr).

Further, the silicon substrate 103, preprocessed in the preprocessingstep conducted immediately before by a diluted hydrofluoric treatmentfor terminating the dangling bonds of silicon on the surface byhydrogen, is introduced into the processing chamber 101 and is placed onthe stage 104 having a heating mechanism. Further, the temperature ofthe specimen is set to 400° C.

Next, a microwave of 2.45 GHz frequency is supplied to the radial lineslot antenna 106 from the coaxial waveguide 105 for 1 minute, whereinthe microwave thus supplied is introduced into the processing chamber107 from the radial lien slot antenna 106 through the dielectric plate107. Thereby, there is formed high-density plasma of Kr in theprocessing chamber 101. The surface-terminating hydrogen is thus removedby exposing the surface of the silicon substrate 103 to the plasma thusexcited on the Kr gas.

Next, in the step of FIG. 16B, the pressure of the processing chamber101 is maintained at about. 133 Pa (1 Torr) and a mixed gas of Kr/O₂/NH₃is introduced from the shower plate 103 with the partial pressure ratioof 96.5/3/0.5. Thereby, a silicon oxynitride film 103E is formed on thesilicon surface with the thickness of 3.5 nm. Upon formation of thesilicon oxynitride film of the desire film thickness, the supply of themicrowave power is shutdown and the plasma excitation is terminated.Further, the Kr/O₂/NH₃ mixed gas is replaced with the Ar gas and theoxynitridation processing is terminated.

Next, in the step of FIG. 16C, the oxynitride film 103E thus formed isused for the gate insulation film, and a gate electrode 103F is formedon the gate insulation film 103E. Further, by conducting variouspatterning processes, ion implantation processes, passivation filmformation processes, hydrogen sintering processes, and the like, areconducted, and a semiconductor integrated circuit device havingtransistors and capacitors is obtained.

FIG. 17 shows the relationship between the density of atomic stateoxygen O* formed in the processing apparatus of FIG. 5 measured byphotoemission analysis and the mixing ratio of the NH₃ gas in theKr/O₂/NH₃ gas.

Referring to FIG. 17, the density of the atomic state oxygen O* asmeasured by the photoemission analysis does not change substantiallywhen the mixing ratio of the Kr/O₂/NH₃ gas is in the range of97/3/0-95/3/2, while when the ratio of NH₃ is increased further, theformation of the atomic state oxygen O* is reduced and the amount of theatomic state hydrogen is increased. Particularly, in the oxynitride filmobtained in the case the mixing ratio of the Kr/O₂/NH₃ gas is about96.5/3/0.5, it can be seen that the leakage current becomes minimum andboth of the breakdown voltage and the resistance against electric chargeinjection are improved.

FIG. 18 shows the concentration distribution of silicon, oxygen andnitrogen in the oxynitride film of the present embodiment as measured bya secondary ion mass spectrometer, wherein the horizontal axis of FIG.18 shows the depth as measured from the surface of the oxynitride film.In FIG. 18, it can be seen that the distribution of silicon, oxygen andnitrogen is changing gently in the film, while this merely meansnon-uniformity of etching and does not mean that the thickness of theoxynitride film is non-uniform.

Referring to FIG. 18, it can be seen that the concentration of nitrogenin the oxynitride film is large at the silicon/silicon oxynitride filminterface and also at the silicon oxynitride film surface and decreasesat the central part of the oxynitride film. Thereby, it should be notedthat the amount of nitrogen incorporated into the oxynitride film isseveral ten percent as compared with silicon or oxygen. As will beexplained later, the nitrogen concentrating to the silicon/siliconoxynitride film interface in the silicon oxynitride film of FIG. 18 isthought as relaxing the stress at such an interface. As a result of suchstress relaxation, the trapping of electric charges in the film or thedensity of interface states caused by the stress is reduced in thesilicon oxynitride film of FIG. 18, and this contributes to thereduction of the leakage current.

FIG. 19 shows the dependence of leakage current of the oxynitride filmof the present embodiment on the applied electric field, wherein FIG. 19also shows the leakage current characteristic of the oxide film of thesame film thickness in which the exposure process to the Kr plasma isomitted before the oxide film formation process by the microwave plasmaand further the leakage current characteristic of the oxide film formedby a thermal oxidation process for the purpose of comparison.

Referring to FIG. 19, it can be seen that the value of the leakagecurrent at the same electric field is reduced by the order of 2-4 in theoxynitride film of the present embodiment in which the oxynitridationprocessing is conducted by introducing the Kr/O₂/NH₃ gas after removingthe terminating hydrogen by the Kr plasma irradiation as compared withthe oxide film formed by the conventional process and that theoxynitride film thus formed has excellent low-leakage characteristics.

In FIG. 10 explained before, it should be noted that the relationship ofthe leakage current characteristic and the film thickness of theoxynitride film thus formed is represented by ▪.

Referring to FIG. 10 again, the oxynitride film formed by the presentembodiment after conducting the Kr irradiation has a similar leakagecharacteristic to the oxide film formed with a similar process and thatthe leakage current is only 1×10⁻² A/cm² also in the case the filmthickness is bout 1.6 nm.

It should be noted that the oxynitride film f the present embodimentalso showed excellent electric properties and reliability such asbreakdown characteristic and hot carrier resistance superior to theoxide film of the first embodiment explained before. Further, there wasobserved no dependence on the surface orientation of the siliconsubstrate, and thus, it becomes possible to form a gate insulation filmof excellent characteristic not only on the (100) surface of silicon butalso on the silicon surface of any surface orientation.

As explained above, it becomes possible to form a silicon oxynitridefilm of superior characteristics and film quality on the silicon surfaceof any surface orientation at the low temperature of 400° C. byconducting the silicon oxynitridation processing by using the Kr/O₂/NH₃high-density plasma, after removing the surface-terminating hydrogen.

The reason why such advantageous effect can be achieved by the presentembodiment is attributed not only to the reduction of hydrogen contentin the oxynitride film caused by removal of the surface-terminatinghydrogen but also to the effect of the nitrogen contained in theoxynitride film with a proportion of several ten percent or less. In theoxynitride film of the present embodiment, the content of Kr is about1/10 or less as compared with the oxide film of the first embodiment,and in place of Kr, the film contains a large amount of nitrogen. Thus,in the present embodiment, it is believed that the reduction of hydrogenin the oxynitride film causes reduction of weak bonds in the siliconoxynitride film, while the existence of nitrogen in the film causedrelaxation of stress in the film or at the Si/SiO₂ interface. As aresult of this, the number of trapped electrical charges in the film orthe surface state density is reduced, and the electric properties of theoxynitride film is improved significantly. Particularly, it is believedthe reduction of hydrogen concentration level in the oxynitride film to10²² cm⁻² or less, more preferably 10¹¹ cm⁻² or less and the existenceof nitrogen in the film with a proportion of several ten percent withrespect to silicon or oxygen contribute to the improvement of theelectric properties and reliability of the silicon oxynitride film.

In the present embodiment, the supply of the microwave power is shutdownat the end of the oxynitridation processing upon formation of thesilicon oxynitride film with the predetermined thickness, and theKr/O₂/NH₃ mixed gas is replaced with the Ar gas. On the other hand, itis possible to terminate the oxynitridation processing by introducing aKr/NH3 mixed gas with the partial pressure ratio of 98/2 from the showerplate 103 before the shutdown of the microwave power while maintainingthe pressure at 133 Pa (1 Torr) and form a silicon nitride film on thesurface of the silicon oxynitride film with the thickness of about 0.7nm. According to this process, a silicon nitride film is formed on thesurface of the silicon oxynitride film and an insulation film having ahigher dielectric constant is obtained.

In the oxynitride film of the present embodiment, it should be notedthat the concentration of nitrogen to the silicon/oxynitride filminterface and the concentration of nitrogen to the surface of theoxynitride film explained with reference to FIG. 18 are maintainedduring the growth of the oxynitride film.

FIG. 20 shows the change of the nitride distribution profile with thegrowth of the oxynitride film schematically.

Referring to FIG. 20, nitrogen concentrate to the surface of theoxynitride film and to the interface between the oxynitride film and theunderlying silicon substrate, and this tendency is maintained even whenthe oxynitride film has made a growth. As a result, the oxynitride film,while having an overall composition of an oxynitride film, does have acomposition near an oxide film in the mid depth part of the film and acomposition near a nitride film at the surface as well at the interfacebetween the oxynitride film and the substrate. Further, the depth ofpenetration of nitrogen at the oxynitride film is limited to 2-3 nm orless, and thus, the thickness of the nitride film formed on the surfaceof the oxynitride film is limited to 2-3 nm.

FIFTH EMBODIMENT

Next, formation process of a semiconductor device according to a fifthembodiment of the present invention will be described wherein thesemiconductor device includes a high-quality silicon oxide film formedon a corner part of the device isolation sidewall that constitutes ashallow-trench isolation or on a silicon surface having an undulatingsurface, form.

FIG. 21A shows the concept of shallow trench isolation.

Referring to FIG. 21A, the illustrated shallow trench isolation isformed by forming an isolation trench on a surface of a siliconsubstrate 1003 by conducting a plasma etching process, filling thetrench thus formed with a silicon oxide film 1002 formed by a CVDprocess, and planarizing the silicon oxide film 1002 by a CMP process,and the like.

In the present embodiment, the silicon substrate is exposed to anoxidizing atmosphere at 800-900° C. after the polishing step of thesilicon oxide film 1002 to conduct sacrifice oxidation process, and thesilicon oxide film thus formed as a result of the sacrifice oxidationprocess is etched away in a chemical solution containing hydrofluoricacid. Thereby, a silicon surface terminated with hydrogen is obtained.In the present embodiment, a procedure similar to the one explained inthe first embodiment is conducted and the surface-terminating hydrogenis removed by using the Kr plasma. Thereafter, the Kr/O2 gas isintroduced and the silicon oxide film is formed with the thickness ofabout 2.5 nm.

According to the present embodiment, the silicon oxide film is formedwith a uniform thickness even on the corner part of the shallow trenchisolation without causing decrease of silicon oxide film thickness. Thesilicon oxide film thus formed by the plasma oxidation process whileusing the Kr plasma has excellent QBD (charge-to-breakdown)characteristics including the shallow trench isolation part, and thereis caused no increase of leakage current even in the case the injectedelectric charges are 10²C/cm². Thus, the reliability of the device isimproved significantly.

In the case of forming the silicon oxide film by the conventionalthermal oxidation process, the thickness of the silicon oxide film isseverely reduced at the corner part of the shallow trench isolation withincreasing taper angle of the shallow trench isolation, while in thecase of the present invention, no such thinning of the silicon oxidefilm is caused at such a corner part of the shallow trench isolationeven in the case the taper angle is increased. Thus, in the presentembodiment, the use of a near rectangular taper angle for the trench ofthe shallow trench isolation structure enables reduction of the area ofthe device isolation region, and further increase of integration densitybecomes possible in the semiconductor device. It should be noted thatthe taper angle of about 70 degrees has been used for the deviceisolation part in the conventional technology, which relies on thethermal oxidation process, because of the limitation caused by thethinning of the thermal oxide film at the trench corner part as shown inFIG. 21B. According to the present invention, it becomes possible to usethe angle of 90 degrees.

FIG. 22 shows the cross-sectional view of the silicon oxide film formedon a silicon surface in which an undulating surface morphology is formedby conducting a 90-degree etching, with a thickness of 3 nm according tothe procedure of the first embodiment.

Referring to FIG. 22, it can be seen that a silicon oxide film ofuniform thickness is formed on any of the surfaces.

The oxide film formed as such has excellent electric properties such asexcellent leakage current or breakdown characteristic, and thus, thepresent invention can realize a high-density semiconductor integratedcircuit having a silicon three-dimensional structure, which may includeplural surface orientations as in the case of a vertical structure.

SIXTH EMBODIMENT

FIG. 23 shows the construction of a flash memory device 20 according toa sixth embodiment of the present invention, wherein those partscorresponding to the parts described before are designated by the samereference numerals and the description thereof will be omitted.

Referring to FIG. 23, the flash memory device 20 of the presentembodiment uses the dielectric film 12A of the third embodiment or thefourth embodiment, for the tunneling insulation film 12.

FIG. 24 shows the state in which a write voltage is applied to hecontrol gate electrode 15 in the flash memory device 20 of FIG. 23.

Referring to FIG. 24, it can be seen that the band structure of thesilicon oxide film and the nitride film constituting the dielectric film12A changes significantly upon application of the write voltage to thecontrol gate electrode 15 due to the corresponding change of potentialof the floating gate electrode 13, and the hot electrons formed in thechannel region 11A are injected into the floating gate electrode 13after passing through the triangular potential formed by the conductionband Ec of the silicon oxide film in the form of Fowler-Nordheimcurrent.

As explained already with reference to FIG. 15, such a dielectric filmforms a thick potential barrier with regard to the conducting electronsin the channel region 11A in the non-writing state of the flash memorydevice 20, and the tunneling current is effectively blocked.

FIG. 25 shows the voltage versus current characteristic of the tunnelinginsulation film 12A of the flash memory device 20 of FIG. 25 insuperposition with the graph of FIG. 3.

Referring to FIG. 25, it can be seen that the tunneling insulation film12A provides a very low leakage current in the case the applied electricfield is small while the tunneling current increases sharply when theapplied electric field is increased in response to application of apredetermined write voltage, and it becomes possible to conductefficient writing of information in short time. Further, in the case ofconducting the writing with the level of conventional injection current,the time needed for writing is reduced.

In the flash memory device 20 of FIG. 23, the stress at the interfacebetween the Si substrate 11 and the tunneling insulation film 12A isrelaxed by using the oxynitride film 103E formed in the process of FIGS.16A-16C for the tunneling insulation film 12A and the quality of thetunneling insulation film 12A is improved. As a result, the leakagecurrent is reduced further. This means that the thickness of thetunneling insulation film 12A can be reduced, and thus, it becomespossible to realize a flash memory operating at low voltage.

SEVENTH EMBODIMENT

Next, a flash memory device according to a seventh embodiment of thepresent invention that uses the low-temperature formation technology ofoxide film and nitride film or the low-temperature formation technologyof oxynitride film by plasma will be explained. In the descriptionbelow, it should be noted that the explanation is made on a flash memorydevice, while it should be noted that the present invention isapplicable also to EPROMs and EEPROMs.

FIG. 26 shows the schematic cross-sectional diagram of a flash memorydevice according to the present embodiment.

Referring to FIG. 26, the flash memory device is constructed on asilicon substrate 1201 and includes a tunneling oxide film 1202 formedon the silicon substrate 1201, a first polysilicon gate electrode 1203formed on the tunneling oxide film 1202 as a floating gate electrode, asilicon oxide film 1204 and a silicon nitride film 1205 formedconsecutively on the polysilicon gate electrode 1203, and a secondpolysilicon gate electrode 1206 formed on the silicon nitride film 1205as a control gate electrode. In FIG. 26, illustration of the sourceregion, drain region, contact hole, interconnection patterns, and thelike, is omitted. It should be noted that the silicon oxide film 1202 isformed by the silicon oxide film formation method explained withreference to the first embodiment, while the laminated structure of thesilicon oxide film 1204 and the nitride film 1205 is formed by theformation method of silicon nitride film explained in relation to thethird embodiment.

FIGS. 27-30 are schematic diagrams explaining the fabrication process ofthe flash memory device of the present embodiment step by step.

Referring to FIG. 27, a silicon substrate 1301 includes a flash memorycell region A, a high-voltage transistor region B and a low-voltagetransistor region C such that the regions A-C are defined by a fieldoxide film 1302, wherein a silicon oxide film 1303 is formed on thesurface of the silicon substrate 1301 in each of the regions A-C. Thefield oxide film 1302 may be formed by a selective oxidation process(LOCOS method) or shallow trench isolation method.

In the present embodiment, Kr is used for the plasma excitation gas forthe removal of the surface-terminating hydrogen or for the formation ofthe oxide film and the nitride film. The same apparatus explained withreference to FIG. 5 is used for the formation of the oxide film and thenitride film.

Next, in the step of FIG. 28, the silicon oxide film 1303 is removedfrom the memory cell region A and the silicon surface is terminated byhydrogen by conducting the cleaning process in a hydrochloric acidsolution. Further, a tunneling oxide film 1304 is formed similarly thefirst embodiment before.

Thus, the vacuum vessel (processing chamber) 101 is evacuated to thevacuum state similarly to the first embodiment and the Ar gas isintroduced into the processing chamber 101 from the shower plate 102.Next, the Ar gas is switched to the Kr gas and the pressure inside theprocessing chamber 101 is set to about 1 Torr.

Next, the silicon oxide film 1303 is removed and the hydrofluoric acidtreatment is applied to the silicon substrate. The silicon substrate1301 thus processed is introduced into the processing chamber 101 as thesilicon substrate 103 of FIG. 5 and is placed on the stage 104 equippedwith the heating mechanism. Further, the temperature of the substrate isset to 400° C.

Further, a microwave of 2.45 GHz frequency is supplied from the coaxialwaveguide 105 to the radial line slot antenna 106 for 1 minute, whereinthe microwave thus supplied is introduced into the processing chamber101 from the radial line slot antenna 106 through the dielectric plate107. By exposing the surface of the silicon substrate to thehigh-density Kr plasma thus formed in the processing chamber 101, theterminating hydrogen are removed from the silicon surface of thesubstrate 1301.

Next, the Kr gas and the O₂ gas are introduced from the shower plate102, and a silicon oxide film 1304 used for the tunneling insulationfilm is formed on the region A with a thickness of 3.5 nm. Next, a firstpolysilicon layer 1305 is deposited so as to cover the silicon oxidefilm 1304.

Next, the first polysilicon layer 1305 is removed from the regions B andC for the high voltage and low voltage transistors by a patterningprocess, such that the first polysilicon pattern 1305 is left only onthe tunneling oxide film 1304 in the memory cell region A.

After this etching process, a cleaning process is conducted and thesurface of the polysilicon pattern 1305 is terminated with hydrogen.

Next, in the step of FIG. 29, an insulation film 1306 having an ONstructure and including a lower oxide film 1306A and an upper nitridefilm 1306B therein is formed so as to cover the surface of thepolysilicon pattern 1305 similarly to the third embodiment.

More specifically, this ON film is formed as follows.

The vacuum vessel (processing chamber) 101 is evacuated to a vacuumstate and the AR gas supplied from the shower plate 102 is switched tothe Kr gas. Further, the pressure inside the processing chamber is setto about 133 Pa (1 Torr). Next, the silicon substrate 1301 carryingthereon the polysilicon pattern 1305 in the state that the hydrogentermination is made is introduced into the processing chamber 101 and isplaced on the stage 104 having the heating mechanism. Further, thetemperature of the specimen is set to 400° C.

Next, a microwave of 2.45 GHz frequency is supplied to the radial lineslot antenna 106 from the coaxial waveguide 105 for about 1 minute.Thereby, the microwave is introduced into the processing chamber 101from the radial line slot antenna 106 through the dielectric plate 107,and there is formed a high-density Kr plasma. As a result, the surfaceof he polysilicon pattern 1305 is exposed to the Kr gas and the surfaceterminating hydrogen is removed.

Next, a Kr/O2mixed gas is introduced into the processing chamber 101from the shower plate 102 while maintaining the pressure of theprocessing chamber 101 to 133 Pa (1 Torr), and a silicon oxide film isformed on the polysilicon surface with a thickness of 3 nm.

Next, the supply of the microwave is shutdown temporarily andintroduction of the Kr gas and the O₂ gas is interrupted. Next, theinterior of the vacuum vessel (processing chamber) 101 is evacuated andthe Kr gas and an NH₃ gas are introduced from the shower plate 102. Thepressure inside the processing chamber 101 is set to about 13.3 Pa (100mTorr) and the microwave of 2.45 GHz is supplied again into theprocessing chamber 101 via the radial line slot antenna. Thereby,high-density plasma is formed in the processing chamber and a siliconnitride film is formed on the silicon oxide film surface with thethickness of 6 nm.

Thus, there is formed an ON film with a thickness of 9 nm, wherein itshould be noted that the ON film thus obtained was extremely uniformcharacterized by a uniform film thickness, and no dependence on thepolysilicon surface orientation was observed.

After such a process of formation of the ON film, the insulation film1306 is removed from the regions B and C for the high-voltage andlow-voltage transistors by conducting a patterning process in the stepof FIG. 30, and ion implantation is conducted into the foregoing regionsB and C of the high-voltage and low-voltage transistors for thresholdcontrol. Further, the oxide film 1303 is removed from the regions B andC and a gate oxide film 1307 is formed on the region B with a thicknessof 5 nm. Thereafter, a gate oxide film 1308 is formed on the region Cwith a thickness of 3 nm.

After this, a second polysilicon layer 1309 and a silicide layer 1310are formed consecutively on the entire structure including the fieldoxide film 1302, and there are formed gate electrodes 1311B and 1311Crespectively in the high-voltage transistor region B and the low-voltagetransistor region C by patterning the second polysilicon layer 1309 andthe silicide layer 1310. Further, there is formed a gate electrode 1311Ain correspondence to the memory cell region A.

After the step of FIG. 30, source and drain regions are formed accordingto a standard semiconductor process, and the device is completed byfurther conducting formation of interlayer insulation films and contactholes and formation of wiring patterns.

In the present invention, it should be noted that the insulation films1306A or 1306B maintains excellent electric properties even when thethickness thereof is reduced to about one half the conventionalthickness of the oxide film or nitride film. Thus, these silicon oxidefilm 1306A and silicon nitride film 1306B maintains excellent electricproperties even when the thickness thereof is reduced. Further, thesefilms are dense and have high quality. Further, it should be noted that,because the silicon oxide film 1306A and the silicon nitride film 1306Bare formed at low temperature, there arises no problem of thermal budgetat the interface between the polysilicon gate and the oxide film, andexcellent interface is realized.

The flash memory device of the present invention can perform the writingand erasing of information at low voltage, and because of this, theformation of substrate current is suppressed. Thereby, deterioration ofthe tunneling insulation film is suppressed. Thus, it becomes possibleto produce a non-volatile semiconductor memory with high yield byarranging the flash memory of the present invention in a two-dimensionalarray. The non-volatile semiconductor memory apparatus thus formed showsstable characteristics.

Thus, the flash memory device of the present invention is characterizedby small leakage current due to the excellent film quality of theinsulation films 1306A and 1306B. Further, it becomes possible to reducethe film thickness without increasing the leakage current. Thus, itbecomes possible to perform the writing operation or erasing operationat an operational voltage of about 5 V. As a result, the memoryretention time of the flash memory device is increase by the order of 2or more as compared with the conventional device, and the number ofpossible rewriting operation is increase by the order of 2 or more.

It should be noted that the film structure of the insulation film 1306is not limited to the ON structure explained above but it is alsopossible to use an O structure formed of an oxide film similar to thatof the first embodiment or an N structure that uses a nitride filmsimilar to the case of the second embodiment. Further, it is possible touse an oxynitride film similar to the one shown in the fourthembodiment. Further, the insulation film 1306 may have an NO structureformed of a nitride film and an oxide film or an ONO structure in whichan oxide film, a nitride film and an oxide film are laminatedconsecutively. Further, the insulation film 1306 may have an NONOstructure in which a nitride film, an oxide film, a nitride film and anoxide film are laminated consecutively. Choice of any of the foregoingstructures can be made according to the purpose from the viewpoint ofcompatibility with the gate insulation film used in the high voltagetransistor or low voltage transistor in the peripheral circuit or fromthe viewpoint of possibility of shared use.

EIGHTH EMBODIMENT

It should be noted that the formation of the gate insulation film byusing the foregoing Kr/O₂ microwave-excited high-density plasma or theformation of the gate nitride film by using the Ar (or Kr)/NH₃ (orN₂/H₂) microwave-excited high-density plasma, is advantageous to theformation of a semiconductor integrated circuit device on asilicon-on-insulator wafer including a metal layer in the underlyingsilicon (metal-substrate SOI). It should be noted that the use of hightemperature process is not possible in such a metal-substrate SOI.Particularly, the effect of removal of the terminating hydrogen appearsconspicuously in the SOI structure having a small silicon thickness andperforming completely depleted operation.

FIG. 31 shows the cross-section of a MOS transistor having ametal-substrate SOI structure.

Referring to FIG. 31, 1701 is a low-resistance semiconductor layer ofn+-type or p+-type, 1702 is a silicide layer such as NiSi, 1703 is aconductive nitride layer such as TaN or TiN, 1704 is a metal layer suchas Cu, and the like, 1705 is a conductive nitride film such as TaN orTiN, 1706 is a low-resistance semiconductor layer of n+-type or p+-type,1707 is a nitride insulation film such as AlN, Si₃N₄, and the like, 1708is an SiO₂ film, 1709 is an SiO₂ layer or a BPSG layer or an insulationlayer combining these, 1710 us a drain region of n+-type, 1711 us asource region of n+-type, 1712 is a drain region of p+-type, 1713 is asource region of p+-type, 1714 and 1715 are silicon semiconductor layersoriented in the <111> direction, 1716 is an SiO₂ film formed by theKr/O₂ microwave-excited high-density plasma after removing thesurface-terminating hydrogen by the procedure of the first embodiment ofthe present invention, 1717 and 1718 are respectively the gateelectrodes of an n-MOS transistor and a p-MOS transistor and formed ofTa, Ti, TaN/Ta, TiN/Ti, and the like, 1719 is a source electrode of then-MOS transistor, and 1720 is a drain electrode of the n-MOS transistorand a p-MOS transistor. Further, 1721 is a source electrode of a p-MOStransistor and 1722 is a substrate surface electrode.

In such a substrate including a Cu layer and protected by TaN or TiN,the temperature of thermal processing has to be about 700° C. or lessfor suppressing diffusion of Cu. Thus, the source or drain region ofn+-type or p+-type is formed by conducting a thermal annealing processat 550° C. after ion implantation process of As+, AsF₂+ or BF₂+.

In the semiconductor device having the device structure of FIG. 31, itshould be noted that the comparison of the transistor sub-thresholdcharacteristics between the case the gate insulation film is formed by athermal oxide film and the case the gate insulation film is formed bythe Kr/O₂ microwave-excited high-density plasma after removing thesurface-terminating hydrogen by conducting the Kr plasma irradiationprocess, has revealed the fact that there appears kink or leakage in thesub-threshold characteristics when the gate insulation film is formed bythe thermal oxidation process, while in the case the gate insulationfilm is formed by the present invention, excellent sub-thresholdcharacteristics are obtained.

In the case a mesa-type device isolation structure is used, it should benoted that there appears a silicon surface having a surface orientationdifferent from that of the silicon surface forming the flat part, at thesidewall part of the mesa device isolation structure. By forming thegate insulation film by the plasma oxidation process while using Kr, theoxidation of the mesa device isolation sidewall is achieved generallyuniformly similarly to the flat part, and excellent electric propertiesand high reliability are achieved.

Further, it becomes possible to form a metal-substrate SOI integratedcircuit device having excellent electric properties and high reliabilityalso in the case of using a silicon nitride film formed by Ar/NH₃according to the procedure of the second embodiment for the gateinsulation film.

In the present embodiment, too, it is possible to obtain excellentelectric characteristics even in the case the thickness of the siliconnitride film is set to 3 nm (1.5 nm in terms of silicon oxide filmequivalent thickness), and the transistor drivability is improved byabout twice as compared with the case of using a silicon oxide film of 3nm thickness.

NINTH EMBODIMENT

FIG. 32 schematically shows an example of the fabrication apparatusaccording to an eighth embodiment of the present invention intended toconduct oxidation processing, nitridation processing or oxynitridationprocessing on a large rectangular substrate such as a glass substrate ora plastic substrate on which liquid crystal display devices or organicelectro-luminescence devices are formed.

Referring to FIG. 32, a vacuum vessel (processing chamber) 1807 isevacuated to a low pressure state and a Kr/O₂ mixed gas s introducedfrom a shower plate 1801 provided in the processing chamber 1807.Further, the processing chamber 1807 is evacuated by a lead screw pump1802 such that the pressure inside the processing chamber 1807 is set to133 Pa (1 Torr). Further, a glass substrate 1803 is placed on a stage1804 equipped with a heating mechanism, and the temperature of the glasssubstrate is set to 300° C.

The processing chamber 1807 is provided with a large number ofrectangular waveguides 1805 and a microwave is introduced into theprocessing chamber 1807 from respective slits of the foregoingrectangular waveguides 1805 via a dielectric plate 1806, andhigh-density plasma is formed in the processing chamber 1807. Thereby,the shower plate 1801 provided in the processing chamber 1807 functionsalso as a waveguide for propagating the microwave emitted by thewaveguide in the right and left directions in the form of a surfacewave.

FIG. 33 shows an example of a polysilicon thin film transistor (TFT)used for driving a liquid crystal display device or an organic ELphotoemission device or for use in a processing circuit, wherein itshould be noted that the polysilicon thin film transistor of FIG. 33 isformed by using the gate oxide film or gate nitride film of the presentinvention while using the apparatus of FIG. 32.

First, the example of using a silicon oxide film will be explained.

Referring to FIG. 33, 1901 is a glass substrate, 1902 is a Si₃N₄ film,1903 is a channel layer of a polysilicon n-MOS transistor having apredominantly (111) orientation, 1905 and 1906 are respectively a sourceregion and a drain region of the polysilicon n-MOS transistor, 1904 is achannel layer of a polysilicon p-MOS transistor having a predominantly(111) orientation, and 1907 and 1908 are respectively a source regionand a drain region of the polysilicon p-channel MOS transistor. Further,1901 is a gate electrode of the polysilicon n-MOS transistor while 1911is a gate electrode of the polysilicon p-MOS transistor, 1912 is aninsulation film such as SiO₂, BSG or BPSG, 1913 and 1914 arerespectively the source electrode of the polysilicon n-MOS transistor(and simultaneously the drain electrode of the polysilicon p-MOStransistor), and 1915 is the source electrode of the polysilicon p-MOStransistor.

It should be noted that a polysilicon film formed on an insulation filmtakes a stable state when having the (111) surface orientation in thedirection perpendicular to the insulation film. In this state, thepolysilicon film is dense and well crystallized and thus provides highquality. In the present embodiment, it should be noted that 1909 is asilicon oxide film layer of the present invention formed by theprocedure similar to the one explained with reference to the firstembodiment by using the apparatus of FIG. 32 and has a thickness of 0.2μm. The oxide film 1909 is formed on the (111) oriented polysilicon at400° C. with a thickness of 3 nm.

According to the present invention, there occurred no thinning of oxidefilm at the sharp corner part of the device isolation region formedbetween the transistors, and it was confirmed that the silicon oxidefilm is formed with uniform film thickness on the polysilicon film inany of the flat part and edge part. The ion implantation process forforming the source and drain regions was conducted without passing theions through the gate oxide film, and the electrical activation was madeat 400° C. As a result, the entire process can be conducted at atemperature of 400° C. or less and formation of transistors becamepossible on a glass substrate. The transistor thus formed had themobility of about 300 cm²/Vsec or more for electrons and about 150cm²/Vsec or more for holes. Further, a voltage of 12V or more wasobtained for the source and drain breakdown voltages and for the gatebreakdown voltage. Further, a high-speed operation exceeding 100 MHzbecame possible in the transistor having the channel length of about1.5-2.0 nm. Further, it was confirmed that the silicon oxide film showedexcellent leakage characteristics and excellent characteristics for theinterface states formed at the polysilicon/oxide film interface.

By using the transistor of the present embodiment, the liquid crystaldisplay devices or organic EL photoemission devices can provide variousadvantageous features such as large display area, low cost, high-speedoperation, high reliability, and the like.

While the present embodiment is the one in which the gate insulationfilm or the gate nitride film of the present invention is applied to apolysilicon, the present embodiment is applicable also to the gate oxidefilm or gate insulation film of an amorphous silicon thin-filmtransistor (TFT) or staggered-type thin-film transistor (TFT), which isused in a liquid crystal display device and the like.

TENTH EMBODIMENT

Next, an embodiment of a three-dimensional stacked LSI in which an SOIdevice having a metal layer, a polysilicon device and an amorphoussilicon device are stacked will be described.

FIG. 34 show the cross-section of the three-dimensional LSI of thepresent invention schematically.

Referring to FIG. 34, 2001 is a first SOI device and wiring layer, 2002is a second SOI device and a wiring layer, 2003 is a first polysilicondevice and a wiring layer, 2004 is a second polysilicon device and awiring layer, while 2005 is a layer of an amorphous semiconductor deviceand a functional-material device and includes a wiring layer thereof.

In the first SOI and wiring layer 2001 and also in the second SOI andwiring layer 2002, there are formed various parts such as digitalprocessing parts, high-precision and high-speed analog parts,synchronous DRAM parts, power supply parts, interface circuit parts, andthe like, by using the SOI transistors explained with reference to theseventh embodiment.

In the first polysilicon device and wiring layer 2003, there are formedvarious parallel digital processing parts, inter-functional blockrepeater parts, memory device parts, and the like, by using thepolysilicon transistors or flash memories explained with reference tothe sixth or eighth embodiments together with the wiring layer of thefirst polysilicon device layer 2003.

In the second polysilicon device and wiring layer 2004, there are formedparallel analog processing parts such as an amplifier, A/D converter,and the like, by using the polysilicon transistor explained withreference to the eighth embodiment. Further, optical sensors, soundsensors, touch sensors, wireless transceiver parts, and the like, areformed in the amorphous semiconductor device/functional-material deviceand wiring layer 2005.

The signals formed by the optical sensors, sound sensors, touch sensors,wireless transceiver parts, and the like, provided in the amorphoussemiconductor device/functional-material and wiring layer 2005 areprocessed by the parallel analog processing part such as an amplifier orA/D converter in the second polysilicon device and wiring layer 2004,and are forwarded further to the parallel digital processing parts andthe memory device parts formed in the second polysilicon device andwiring layer 2004 by the polysilicon transistors and flash memorydevices. The signals thus processed are then processed by the digitalprocessing parts, high-precision and high-speed analog parts or thesynchronous DRAM parts provided in the first SOI and wiring layer 2001or second SOI and wiring layer 2002 by using the SOI transistors.

Further, the inter-functional block repeater part provided in the firstpolysilicon device and the wiring layer 2003 does not occupy a largearea even when provided with plural numbers, and it is possible toachieve synchronization of signals all over the LSI.

It should be noted that such a three-dimensional LSI has become possibleas a result of the technology explained in detail with reference to theembodiments.

INDUSTRIAL APPLICABILITY

According to the present invention, it becomes possible to form atunneling oxide film on a silicon surface such as a silicon substrate inthe form that an oxide film and a nitride film are laminated or anitride film and an oxide film and a nitride film are laminatedconsecutively such that the tunneling oxide film as a whole as thecomposition of an oxynitride film. Thereby, the leakage current isreduced significantly while simultaneously reducing the film thickness.With this, it becomes possible to increase the tunneling current densityof a flash memory device, and the like, at the time of writing, and theoperational speed is improved. Further, the operational voltage isreduced.

What is claimed is:
 1. A method of forming a dielectric film,comprising: removing surface-terminated hydrogens from a surface byexposing the surface to a high-density Kr plasma or to low energy Arions; forming a silicon oxide film on the surface; and modifying asurface of said silicon oxide film by exposing the same to hydrogennitride radicals NH* in the absence of a Si-containing gas.
 2. Themethod of forming a dielectric film as claimed in claim 1, wherein saidhydrogen nitride radicals NH* are formed by a microwave plasma formed ina mixed gas of an inert gas selected from the group consisting of Ar andKr and a gas containing nitrogen and hydrogen.
 3. The method of forminga dielectric film as claimed in claim 2, wherein said microwave plasmahas an electron density of 10¹² cm⁻² or more at said surface.
 4. Themethod of forming a dielectric film as claimed in claim 2, wherein saidmicrowave plasma has a plasma potential of 10V or less at said surface.5. The method of forming a dielectric film as claimed in claim 2,wherein said gas containing nitrogen and hydrogen comprises an NH₃ gas.6. The method of forming a dielectric film as claimed in claim 1,wherein said surface comprises a silicon surface and said oxide film isformed by oxidation of said silicon surface.
 7. The method of forming adielectric film as claimed in claim 6, wherein said oxidation of saidsilicon surface is conducted by exposing said silicon surface tomicrowave plasma formed in a mixed gas of an inert gas predominantly ofKr and a gas containing oxygen as a constituent element.
 8. The methodof forming a dielectric film as claimed in claim 6, wherein said siliconoxide film is formed by thermal oxidation of said surface.
 9. A methodof forming a dielectric film, comprising: removing surface-terminatedhydrogens from a surface by exposing the surface to a high-density Krplasma or to low energy Ar ions; forming a silicon oxide film on thesurface; and modifying a surface of said silicon oxide film by exposingthe same to microwave plasma formed in a mixed gas of an inert gasselected from the group consisting of Ar and Kr and a gas containingnitrogen and hydrogen in the absence of a Si-containing gas.
 10. Themethod of forming a dielectric film as claimed in claim 9, wherein saidmicrowave plasma has an electron density of 10¹² cm⁻³ or more at saidsurface.
 11. The method of forming a dielectric film as claimed in claim9, wherein said microwave plasma has a plasma potential of 10V or lessat said surface.
 12. The method of forming a dielectric film as claimedin claim 9, wherein said gas containing said nitrogen and hydrogen asconstituent elements comprises a NH₃ gas.
 13. The method of forming adielectric film as claimed in claim 9, wherein said surface comprises asilicon surface and wherein said oxide film is formed by oxidation ofsaid silicon surface.
 14. The method of forming a dielectric film asclaimed in claim 13, wherein said oxidation of said silicon surface isconducted by exposing said silicon surface to a microwave plasma formedin a mixed gas of an inert gas predominantly of Kr and a gas containingoxygen.
 15. The method of forming a dielectric film as claimed in claim13, wherein said silicon oxide film is formed by thermal oxidation ofsaid silicon surface.
 16. A method of forming a dielectric filmcomprising exposing a silicon surface to a high-density Kr plasma or tolow energy Ar ions in order to remove surface-terminated hydrogens fromthe silicon surface to form a clean silicon surface, and exposing theclean silicon surface to a microwave plasma formed in a mixed gas of aninert gas primarily formed of Kr, a gas containing nitrogen and a gascontaining oxygen to form an oxynitride film on said silicon surface.17. The method of forming a dielectric film as claimed in claim 16,wherein said microwave plasma has an electron density of 10¹² cm⁻³ orless at said silicon surface.
 18. The method of forming a dielectricfilm as claimed in claim 16, wherein said microwave plasma has a plasmapotential of 10V or less at said silicon surface.
 19. The method offorming a dielectric film as claimed in claim 16, wherein said gascontaining nitrogen comprises a NH₃ gas, and said gas containing oxygencomprises an O₂ gas.
 20. A method of forming a dielectric filmcomprising exposing a silicon surface to a microwave plasma formed in amixed gas of an inert gas primarily formed of Kr, a NH₃ gas, and an O₂gas to form an oxynitride film on said silicon surface, wherein saidinert gas and said O₂ gas and said NH₃ gas are supplied with a partialpressure ratio of 96.5:3:0.5.
 21. The method of forming a dielectricfilm as claimed in claim 16, wherein said silicon surface is exposed toatomic state oxygen (O*) and hydrogen nitride radicals (NH*) in saidstep of exposing said silicon surface to said microwave plasma.
 22. Amethod of fabricating a semiconductor device, comprising: removingsurface-terminated hydrogens from a silicon substrate by exposing thesilicon substrate to a high-density Kr plasma or to low energy Ar ions;forming a silicon oxide film on the silicon substrate by oxidation;modifying a surface of said silicon oxide film by exposing the same tohydrogen nitride radicals NH* in the absence of a Si-containing gas; andforming a gate electrode on said modified silicon oxide film.
 23. Themethod of fabricating a semiconductor device as claimed in claim 22,wherein said hydrogen nitride radicals (NH*) are formed by microwaveplasma formed in a mixed gas of an inert gas selected from the groupconsisting of Ar and Kr and a gas containing nitrogen and hydrogen. 24.The method of fabricating a semiconductor device as claimed in claim 23,wherein said microwave plasma has an electron density of 10¹² cm⁻³ ormore at said surface of said silicon substrate.
 25. The method offabricating a semiconductor device as claimed in claim 23, wherein saidmicrowave plasma has a plasma potential of 10V or less at said surfaceof said silicon substrate.
 26. The method of fabricating a semiconductordevice as claimed in claim 23, wherein said gas containing nitrogen andhydrogen comprises a NH₃ gas.
 27. The method of fabricating asemiconductor device as claimed in claim 23, wherein said silicon oxidefilm is formed by exposing said silicon surface to a microwave plasmaformed in a mixed gas of an inert gas predominantly of Kr and a gascontaining oxygen.
 28. A method of fabricating a semiconductor device,comprising: removing surface-terminated hydrogens from a siliconsubstrate by exposing the silicon substrate to a high-density Kr plasmaor to low energy Ar ions; forming a silicon oxide film on the siliconsubstrate by oxidation; modifying a surface of said silicon oxide filmby exposing said surface to a microwave plasma formed in a mixed gas ofan inert gas selected from the group consisting of Ar and Kr and a gascontaining nitrogen and hydrogen in the absence of a Si-containing gas,and forming a gate electrode on said modified silicon oxide film. 29.The method of fabricating a semiconductor device as claimed in claim 28,wherein said microwave plasma has an electron density of 10¹² cm⁻³ ormore at said surface of said silicon substrate.
 30. The method offabricating a semiconductor device as claimed in claim 28, wherein saidmicrowave plasma has a plasma potential of 10V or less at said surfaceof said silicon substrate.
 31. The method of fabricating a semiconductordevice as claimed in claim 28, wherein said gas containing nitrogen andhydrogen comprises a NH₃ gas.
 32. The method of fabricating asemiconductor device as claimed in claim 28, wherein said siliconsurface is oxidized by exposing said silicon surface to a microwaveplasma formed in a mixed gas of an inert gas of predominantly Kr and agas containing oxygen.
 33. The method of fabricating a semiconductordevice as claimed in claim 28, wherein said silicon oxide film is formedby thermal oxidation.
 34. A method of fabricating a semiconductordevice, comprising: exposing a silicon substrate surface to ahigh-density Kr plasma or to low energy Ar ions in order to removesurface-terminated hydrogens from the silicon substrate surface to forma clean surface, exposing the clean surface to a microwave plasma formedin a mixed gas of an inert gas primarily formed of Kr, a gas containingnitrogen and a gas containing oxygen in the absence of a Si-containinggas, to form an oxynitride film on said silicon surface; and forming agate electrode on said oxynitride film.
 35. The method of fabricating asemiconductor device as claimed in claim 34, wherein said microwaveplasma has an electron density of 10¹² cm⁻³ or more on said siliconsubstrate.
 36. The method of fabricating a semiconductor device asclaimed in claim 34, wherein said microwave plasma has a plasmapotential of 10V or less on said silicon substrate.
 37. The method offabricating a semiconductor device as claimed in claim 34, wherein saidgas containing nitrogen comprises a NH₃ gas, and said gas containingoxygen comprises an O₂ gas.
 38. A method of fabricating a semiconductordevice comprising: exposing a silicon substrate surface to a microwaveplasma formed in a mixed gas of an inert gas primarily formed of Kr, aNH₃ gas, and an O₂ gas to form an oxynitride film on said siliconsurface; and forming a gate electrode on said oxynitride film, whereinsaid inert gas and said O₂ gas and said NH₃ gas are supplied to apartial pressure ratio of 96.5:3:0.5.
 39. The method of fabricating asemiconductor device as claimed in claim 34, wherein said step ofexposing said silicon surface to said microwave plasma comprisesexposing said silicon surface to atomic state oxygen (O*) and hydrogennitride radicals (NH*).
 40. A method of forming a dielectric film,comprising: forming a silicon oxide film on a surface by terminatingdangling bonds on a silicon surface with hydrogen, removing thesurface-terminating hydrogens, and oxidizing the silicon surface; andmodifying a surface of said silicon oxide film by exposing the same tohydrogen nitride radicals NH*.
 41. A method of forming a dielectricfilm, comprising: forming a silicon oxide film on a surface byterminating dangling bonds on a silicon surface with hydrogen, removingthe surface-terminating hydrogens, and oxidizing the silicon surface;and modifying a surface of said silicon oxide film by exposing the sameto microwave plasma formed in a mixed gas of an inert gas selected fromthe group consisting of Ar and Kr and a gas containing nitrogen andhydrogen.
 42. A method of fabricating a semiconductor device,comprising: forming a silicon oxide film on a silicon substrate byterminating dangling bonds on a silicon surface with hydrogen, removingthe surface-terminating hydrogens, and then oxidizing said surface toform the silicon oxide film; modifying a surface of said silicon oxidefilm by exposing the same to hydrogen nitride radicals NH*; and forminga gate electrode on said modified silicon oxide film.
 43. A method offabricating a semiconductor device, comprising: forming a silicon oxidefilm on a silicon substrate by terminating dangling bonds on a siliconsurface with hydrogen, removing the surface-terminating hydrogens, andthen oxidizing said surface to form the silicon oxide film; modifying asurface of said silicon oxide film by exposing said surface to amicrowave plasma formed in a mixed gas of an inert gas selected from thegroup consisting of Ar and Kr and a gas containing nitrogen andhydrogen; and forming a gate electrode on said modified silicon oxidefilm.
 44. A method of fabricating a semiconductor device, comprising:terminating dangling bonds on a silicon surface with hydrogen, removingthe surface-terminating hydrogens, and exposing the silicon substratesurface to a microwave plasma formed in a mixed gas of an inert gasprimarily formed of Kr, a gas containing nitrogen and a gas containingoxygen, to form an oxynitride film on said silicon surface; and forminga gate electrode on said oxynitride film.
 45. A method of forming adielectric film comprising: removing surface-terminated hydrogens from asurface by exposing the surface to a high-density Kr plasma or to lowenergy Ar ions; forming a silicon oxide film on the surface; andmodifying said silicon oxide film by exposing a surface of said siliconoxide film to hydrogen nitride radicals (NH*) in the absence of asilicon-containing gas.